This invention relates to magnetic resonance apparatus.
Such apparatus can be used for non-invasive internal examinations of patients to produce, for example, cross-sectional internal structural images, and blood flow and spectroscopy data.
In use of such apparatus the part of the patient to be examined is placed in a region of strong static magnetic field to define an equilibrium axis of magnetic alignment in the examination region. A radio frequency (RF) magnetic field is then applied temporarily to the examination region, in a direction orthogonal to the static magnetic field direction, to excite magnetic resonance in material, typically hydrogen protons, in the examination region. The resulting RF signals are detected and analyzed. During this sequence of operations one or more gradients are normally imposed on the static magnetic field in the examination region, e.g. to encode spatially the detected RF signals, or for other purposes such as flow encoding.
In use of such apparatus it is sometimes required to dispose a transducer in the examination region, the transducer being connected to equipment outside the examination region by a lead. Examples of such transducers are microphones and loudspeakers for communication between a patient being examined and a person, e.g. medical staff outside the apparatus, microphones and loudspeakers of an active noise reduction system for reducing disturbance of the patient by noise produced in the magnetic field systems surrounding the patient, and sensors for sensing the condition of the patient e.g. thermometers, and heart rate and respiratory monitors.
One problem which arises with such transducers is that they tend to load the RF fields produced in the examination region, thereby distorting the RF fields and degrading the data obtained by analyzing the detected RF signals.